Efficient removal of organic contaminants in CuS-mediated solid-liquid-interfacial fenton-like system: Role of bimetallic cycle and sulfur species.

The conventional Fenton-like system (Fe(III)/H2O2) is severely limited by the inferior activity of Fe(III) on H2O2 activation to produce highly active species and the sluggish regeneration rate of Fe(II). This work significantly enhanced the oxidative breakdown of the target organic contaminant bisphenol A (BPA) by Fe(III)/H2O2 by introducing cheap CuS at a low dose of 50 mg/L. The BPA removal (20 mg/L) in CuS/Fe(III)/H2O2 system reached 89.5 % within 30 min under the optimal conditions: CuS dosage 50 mg/L, Fe(III) concentration 0.05 mM, H2O2 concentration 0.5 mM and pH 5.6. Compared to CuS/H2O2 and Fe(III)/H2O2 systems, the reaction constants had a 47- and 12.3-fold enhancement, respectively. Even compared with the conventional Fe(II)/H2O2 system, the kinetic constant also increased more than twice, further confirming the distinctive superiority of constructed system. Element species change analyses showed that Fe(III) in solution was adsorbed onto the CuS surface, and then Fe(III) was rapidly reduced by Cu(I) in the CuS lattice. Combining CuS and Fe(III) (in-situ formed CuS-Fe(III) composite) created a robust co-effect on the activation of H2O2. Also, S(-II) and its derivatives, e.g., Sn2- and S0 (as an electron donor), could quickly reduce Cu(II) to Cu(I) and ultimately oxidize to the harmless product SO42-. Notably, a mere 50 µM of Fe(III) was sufficient to maintain enough regenerated Fe(II) to effectively activate H2O2 in CuS/Fe(III)/H2O2 system. In addition, such a system achieved a broad range of pH applications and was more suitable for real wastewater containing anions and natural organic matter. Scavenging tests, electron paramagnetic resonance (EPR), and probes further verified the critical role of •OH. This work provides a new approach to solving the problems of Fenton systems through a solid-liquid-interfacial system design and exhibits considerable application potential in wastewater decontamination.

Electrocatalytic reduction of nitrate by carbon encapsulated Cu-Fe electroactive nanocatalysts on Ni foam.

Electrocatalytic denitrification is an attractive and effective method for complete elimination of nitrate (NO3-). However, its application is limited by the activity and stability of the electrocatalyst. In this work, a novel bimetallic electrode was synthesized, in which N-doped graphitized carbon sealed with Cu and Fe nanoparticles and immobilized them on nickel foam (CuFe NPs@NC/NF) without any chemical binder. The immobilized Cu-Fe nanoparticles not only facilitated the adsorption of the reactant but also enhanced the electron transfer between the cathode and NO3-, thus promoting the electrochemical reduction of NO3-. Therefore, the as-prepared electrode exhibited enhanced electrocatalytic activity for NO3- reduction. The composite electrode with the Cu/Fe molar ratio of 1:2 achieved the highest NO3- removal (79.4 %) and the lowest energy consumption (0.0023 kW h mg-1). Furthermore, the composite electrode had a robust NO3- removal capacity under various conditions. Benefitting from the electrochlorination on the anode, this electrochemical system achieved nitrogen (N2) selectivity of 94.0 %. Moreover, CuFe NPs@NC/NF exhibited good stability after 15 cycles, which should be attributed to the graphitized carbon layer. This study confirmed that CuFe NPs@NC/NF electrode is a promising and inexpensive electrode with long-term stability for electrocatalytic denitrification.

Achieving high-performance electrocatalytic reduction of nitrate by N-rich carbon-encapsulated Ni-Cu bimetallic nanoparticles supported nickel foam electrode.

The cathode with low-energy consumption and long-term stability is pivotal to achieve the conversion of nitrate (NO3-) to nitrogen (N2) by electrocatalytic denitrification. Herein, a binder-free electrode was synthesized by directly immobilizing N-doped graphitized carbon layer-encapsulated NiCu bimetallic nanoparticles on nickel foam (NF) (NiCu@N-C/NF) and served as the cathode for electrocatalytic NO3- reduction. Morphological characterization indicated that Ni and Cu nanoparticles were encapsulated by the N-doped graphitized carbon layer and well-dispersed on the surface of NF. Compared with monometallic composite cathode (Cu@N-C/NF and Ni@N-C/NF), NiCu@N-C/NF exhibited better NO3- removal performance (98.63 %) and lower energy consumption (0.007 kW·h mmol-1), which should be attributed to its strong adsorption ability to NO3- and excellent electron transfer property. Meanwhile, its electrocatalytic performance could be maintained in wide initial NO3- concentration (1.79-7.14 mM) and solution pH (3-11). With the assistance of electrochlorination, the N2 selectivity of electrochemical system was up to 99.89 % in the presence of 0.028 M Cl-. More importantly, NiCu@N-C/NF electrode displayed an ultra-high stability during ten recycling experiments. This study indicated that the binderless composite cathode NiCu@N-C/NF had great potential in electrocatalytic NO3- removal from wastewater.

Sulfide enhances the Fe(II)/Fe(III) cycle in Fe(III)-peroxymonosulfate system for rapid removal of organic contaminants: Treatment efficiency, kinetics and mechanism.

The activation of peroxymonosulfate (PMS) by Fe(II) or Fe(III) for environmental decontamination is severely limited by the low conversion rate from Fe(III) to Fe(II). Here, we found that this puzzling problem could virtually be solved by introducing trace amounts of S2-. With the addition of 0.2 mM S2-, the bisphenol A (BPA) degradation efficiency and total organic carbon (TOC) removal in PMS/Fe(III) system were improved by 3.8 and 6.0 times, respectively. Meanwhile, the kobs and PMS utilization efficiency also markedly increased by 650% and 160%, respectively. The constructed PMS/Fe(III)/S2- system exhibited a good applicability to a wide pH range (3.2 ~ 9.5) and high resistance to humic acid, Cl- and NO3-. The main reactive oxidant species in PMS/Fe(III)/S2- system were identified by scavenging experiments, electron paramagnetic resonance measurement, chemical probe approach, and 18O isotope-labeling technique. The identification results revealed that FeIVO2+ was the primary reactive oxidant species, while •OH, SO4•-, O2•- and 1O2 were also involved in the degradation of BPA. Finally, the generalizability of PMS/Fe(III)/S2- system was evaluated by varying the target pollutants, oxidants, and reducing S species. The construction of PMS/Fe(III)/S2- system provides some insights into the treatment of organic wastewaters containing S2-, e.g., from refineries and tanneries.

Zirconium-modified biochar as the efficient adsorbent for low-concentration phosphate: performance and mechanism.

Achieving advanced treatment of phosphorus (P) to prevent water eutrophication and meet increasingly stringent wastewater discharge standard is an important goal of water management. In this study, a low-cost, high-efficiency phosphate adsorbent zirconium-modified biochar (ZrBC) was successfully synthesized through co-precipitation method, in which the biochar was prepared from the pyrolysis of peanut shell powder. ZrBC exhibited strong adsorption ability to low-concentration phosphate (< 1 mg·L-1) in water, and the phosphate removal reached 100% at the investigated dosage range (0.1-1.0 mg·L-1). The adsorption process could be described well by pseudo-second-order model and Langmuir isotherm model, indicating that the phosphate adsorption by ZrBC was mainly a chemical adsorption and single-layer adsorption process. The calculated static maximum phosphate adsorption capacity was 58.93 mg·g-1 at 25 °C. The ligand exchange between surface hydroxyl groups and phosphate was the main mechanism for the phosphate adsorption on ZrBC. The presence of coexisting anions except for SO42- had little effect on the phosphate removal. At the column experiment, ZrBC showed superior treatment capacities for simulated secondary effluents and the breakthrough time for 0.5 mg·L-1 effluent phosphate concentration reached 190 h. ZrBC highlights the potential as an effective and environment-friendly adsorbent for the removal of low-concentration phosphate from secondary effluents of municipal wastewater treatment plants (WWTPs).

Peroxymonosulfate (PMS) activation by mackinawite for the degradation of organic pollutants: Underappreciated role of dissolved sulfur derivatives.

The internal Fe2+/Fe3+ cycle is important for peroxymonosulfate (PMS) activation by iron-based materials to produce the reactive oxidative species (ROS) for the breakdown of organic contaminants. Previous studies have focused on the contribution of heterogeneous sulfur species to the Fe2+/Fe3+ cycle such as lattice S(-II) and surface SO32- of iron sulfides. In this study, we found that the dissolved S(-II) from mackinawite (FeS) had a substantial contribution to the Fe2+/Fe3+ cycle. Furthermore, the oxidation intermediates of the dissolved S(-II) such as S2O32- and SO32- ions could convert Fe3+ to Fe2+ in solution. The elimination of target organic pollutant bisphenol A (BPA) derived from PMS activation triggered by the dissolved Fe2+ might be enhanced by the equivalent dissolved S(-II) in the FeS/PMS system. These results revealed that previous studies underestimated the significance of PMS activation by dissolved Fe2+ of iron sulfides to organic pollutant degradation. Moreover, SO4•- and •OH were more likely to be the main ROS for BPA degradation in the FeS/PMS system compared with FeO2+. Considering that the metal sulfides have been widely used to activate PMS, H2O2 and peroxydisulfate, this study offers a new perspective on the function of sulfur in these advanced oxidation processes.

[Enhancement Effects and Mechanisms of Microscale Zero Valent Iron on the Performance of Anaerobic Co-digestion of Waste Activated Sludge and Food Waste].

Focusing on low biogas yields in the anaerobic co-digestion of waste activated sludge and food waste, the enhancing effects and mechanisms of microscale zero valent iron (mZVI) on anaerobic co-digestion was investigated. The results indicated that the addition of mZVI enhanced the methanogenesis stage of co-digestion but had no significant effect on the solubilization, hydrolysis, and acidification stages. With a dosage of 10 g·L-1 mZVI, the cumulative methane yield (based on VS) within 15 days reached 238.68 mL·g-1, which was 20.05% higher than the control group. The mechanism analysis showed that mZVI promoted electron transport system (ETS) activity (based on INTF/TS), which increased to 21.50 mg·(g·h)-1 with 10 g·L-1 mZVI compared to 13.43 mg·(g·h)-1 in the control group. Furthermore, mZVI enhanced direct interspecies electron transfer (DIET) between specific bacteria and methanogens. Microbial community analysis demonstrated that the abundance of DIET-related microorganisms, such as Syntrophomonas, Methanosarcina, and Methanobacterium, was higher in presence of mZVI.

Highly selective electrochemical nitrate reduction using copper phosphide self-supported copper foam electrode: Performance, mechanism, and application.

A highly active and selective electrode is essential in electrochemical denitrification. Although the emerging Cu-based electrode has attracted intensive attentions in electrochemical NO3- reduction, the issues such as restricted activity and selectivity are still unresolved. In our work, a binder-free composite electrode (Cu3P/CF) was first prepared by direct growth of copper phosphide on copper foam and then applied to electrochemical NO3- reduction. The resulting Cu3P/CF electrode showed enhanced electrochemical performance for NO3- reduction (84.3%) with high N2 selectivity (98.01%) under the initial conditions of 1500 mg L-1 Cl- and 50 mg N L-1 NO3-. The cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) demonstrated that electrochemical NO3- reduction was achieved through electron transfer between NO3- and Cu0 originated from CF. The in-situ grown Cu3P served as the bifunctional catalyst, the electron mediator or bridge to facilitate the electron-transfer for NO3- reduction and the stable catalyst to produce atomic H* toward NO2- conversion. Meanwhile, the Cu3P/CF remained its electrocatalytic activity even after eight cyclic experiments. Finally, a 2-stage treatment strategy, pre-oxidation by Ir-Ru/Ti anode and post-reduction by Cu3P/CF cathode, was designed for electrochemical chemical oxygen demand (COD) and total nitrogen (TN) removal from real wastewater.

Efficient degradation of bisphenol A via peroxydisulfate activation using in-situ N-doped carbon nanoparticles: Structure-function relationship and reaction mechanism.

A novel in-situ N-doped carbon nanoparticles (NCNs) was prepared through direct pyrolysis of N-rich polyaniline (PANI) without using external N-containing precursor and the as-prepared materials were employed as metal-free peroxydisulfate (PDS) activator for bisphenol A (BPA) degradation. The catalyst derived from PANI carbonization at 900 °C (NCNs-9) displayed the excellent catalytic activity to activate PDS, resulting in 96.0% BPA degradation efficiency within 20 min. The catalytic activity of NCNs was closely related to their structure-composition, and higher graphitic N content and larger BET surface area were beneficial to the generation of reactive oxygen species (ROS). The quenching tests and electron paramagnetic resonance (EPR) demonstrated that BPA degradation in PDS/NCNs system was accomplished via non-radical (1O2) and radical ( ·OH, SO4·-, and O2·-) pathways, in which O2·- was the main ROS. The origin of O2·- was the conversion of dissolved oxygen and the activation of PDS. The possible degradation pathways of BPA were also proposed. This study might provide inspirations to design in-situ N-doped carbon nanoparticles as the PDS activator for efficient degradation of persistent organic compound via advanced oxidation processes (AOPs).

Electro-assisted autohydrogenotrophic reduction of perchlorate and microbial community in a dual-chamber biofilm-electrode reactor.

The electro-assisted autohydrogenotrophic reduction of perchlorate (ClO4-) was investigated in a dual-chamber biofilm-electrode reactor (BER), in which the microbial community was inoculated from natural sediments. To avoid the effect of extreme pH and direct electron transfer on perchlorate reduction, a novel cathode configuration was designed. The pH of the cathode compartment was successfully controlled in the range of 7.2-8.4 during whole experiment. The effective biological autohydrogenotrophic reduction of perchlorate was achieved using hydrogen generated in-situ on the electrode surface, and the removal rate of 10 mg L-1 perchlorate reached 98.16% at HRT of 48 h. The highest perchlorate removal flux reached to 1498.420 mg m-2·d-1 with a 0.410 kW·h g-perchlorate-1 energy consumption. The microbial community evolution in the BER was determined by high-throughput sequencing and the results indicated that the Firmicutes and Bacteroidetes were dominant at phylum level when perchlorate concentration was 10 mg L-1 or lower. And the Proteobacteria became ascendant at the perchlorate concentration of 20 mg L-1. The functional populations for perchlorate reduction were successfully enriched including Nitrosomonas (30%), Thermomonas (9%), Comamonas (8%) and Hydrogenophaga (3%). Meanwhile, the proportion of functional population in biofilm linked to perchlorate concentration. With the increase of influent perchlorate concentration, the perchlorate-reducing bacteria (PRB) were enriched successfully and became ascendant.

Enhanced anaerobic co-digestion of waste activated sludge and food waste by sulfidated microscale zerovalent iron: Insights in direct interspecies electron transfer mechanism.

The enhancement of zerovalent iron (ZVI) on anaerobic digestion (AD) has been proved, but there are still some problems that constrain the large-scale application of ZVI, such as the destruction of cell membrane and the inhibition of methanogenesis led by rapid H2 accumulation. Aiming at these problems, sulfidated microscale zerovalent iron (S-mZVI) was employed to evaluate its effect on anaerobic co-digestion (AcoD) of waste activated sludge (WAS) and food waste (FW). Experimental results showed that S-mZVI promoted the direct interspecies electron transfer (DIET) between specific bacteria and methanogens, resulting in higher methane yield. At S-mZVI 10 g/L, the cumulative methane yield and ETS activity reached 264.78 mL/g-VS and 24.62 mg INTF/(g-TS h), which was 1.33 and 1.83 times that of blank. Microbiological analysis demonstrated that the abundance of DIET-related microorganisms such as Syntrophomonas, Methanosarcina and Methanobacterium increased with the increasing dosage of S-mZVI.

Electrochemical Cr(VI) removal from aqueous media using titanium as anode: Simultaneous indirect electrochemical reduction of Cr(VI) and in-situ precipitation of Cr(III).

In this work, a novel method for complete Cr(Ⅵ) removal was achieved in a single-chamber cell with titanium (Ti) as anode via simultaneous indirect electro-reduction of Cr(Ⅵ) and in-situ precipitation of Cr(Ⅲ). The Cr(Ⅵ) and total Cr removal, and electric energy consumption were optimized as a function of electrochemical reactor, current density, initial Cr(Ⅵ) and chloride (Cl-) concentration, and initial solution pH. The maximum Cr(Ⅵ) and total Cr removal efficiency reached 80.5 and 79.4% respectively within 12 h at current density of 10 mA cm-2 as initial Cr(Ⅵ) concentration was 0.078 mM. Decreasing the initial solution pH was beneficial to Cr(Ⅵ) reduction, but Cr(Ⅲ) precipitation was inhibited, resulting in the poor total Cr removal. The suitable Cl- concentration guaranteed sufficient reducing agents (Ti3+ and Ti2+) for Cr(Ⅵ) removal. The reaction mechanism demonstrated that Ti anode could be corroded to produce Ti3+ and Ti2+, which provided the electrons for reduction of Cr(Ⅵ) to Cr(Ⅲ). Simultaneously, the solid products (Ti2O(6x-y-z+52)Cl2yCr2x(OH)2z(s)) were in-situ formed and precipitated from the solution due to the continuous generation of hydroxyl ion (OH-) from cathode. This study might provide a new electrochemical method with non-precious metal as the electrode for complete Cr(Ⅵ) removal from aqueous media.

Evaluating the effect of biochar on mesophilic anaerobic digestion of waste activated sludge and microbial diversity.

This study compared the effects of sewage sludge-derived pyrochar (PC300, PC500, and PC700) and hydrochar (HC180, HC240, and HC300) on mesophilic anaerobic digestion of waste activated sludge (WAS). It was demonstrated that hydrochar can better promote the methane production compared with pyrochar. The highest accumulative methane yield of 132.04 ±â€¯4.41 mL/g VSadded was obtained with HC180 addition. In contrast, the PC500 and PC700 showed a slightly negative effect on methane production. Sludge-derived HC not only accelerated the solubilization and hydrolysis of sludge floc, but also improved the production of acetic acid and propionate, further resulting in improved methane production. Simultaneously, the syntrophic microbes facilitating direct interspecies electron transfer (DIET) such as Syntrophomonas, Peptococcaceae, Methanosaeta and Methanobacterium bred rapidly with the addition of HCs. These results indicated that the hydrochar is more ideal as the accelerant to promote the methane production from mesophilic anaerobic digestion of WAS than the pyrochar.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation.

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe2O3 and Fe3O4 NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe2O3 NPs, reduced total nitrogen (TN) loss, and reserved more NH4+-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH4+-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Biological perchlorate reduction: which electron donor we can choose?

Biological reduction is an effective method for removal of perchlorate (ClO4-), where perchlorate is transformed into chloride by perchlorate-reducing bacteria (PRB). An external electron donor is required for autotrophic and heterotrophic reduction of perchlorate. Therefore, plenty of suitable electron donors including organic (e.g., acetate, ethanol, carbohydrate, glycerol, methane) and inorganic (e.g., hydrogen, zero-valent iron, element sulfur, anthrahydroquinone) as well as the cathode have been used in biological reduction of perchlorate. This paper reviews the application of various electron donors in biological perchlorate reduction and their influences on treatment efficiency of perchlorate and biological activity of PRB. We discussed the criteria for selection of appropriate electron donor to provide a flexible strategy of electron donor choice for the bioremediation of perchlorate-contaminated water.

Toxicity of sulfide-modified nanoscale zero-valent iron to Escherichia coli in aqueous solutions.

Sulfide-modified nanoscale zero-valent iron (S/nZVI) has been widely studied for groundwater remediation, but the potential environmental risks are poorly understood. This study examined the toxicity of S/nZVI to Escherichia coli in aqueous solutions. The sulfidation could reduce toxicity of nZVI, and S/nZVI exhibited a weaker toxicity at lower Fe/S molar ratio, resulting from the lower Fe0 content and higher sulfate and iron oxide. The toxicity of S/nZVI was significantly alleviated in the presence of N-Acetyl-L-cysteine (a scavenger for reactive oxygen species (ROS)), revealing that the ROS-induced oxidative stress was the principal mechanism. Moreover, Transmission Electron Microscopy images elucidated that the membranes of S/nZVI-treated cells were disrupted and S/nZVI existed on E. coli surface and in the cytoplasm. S/nZVI might have interacted with the amine, carboxyl, and ester groups on E. coli cell surface, as demonstrated by Fourier Transform Infrared Spectroscopy analysis. However, the presence of individual groundwater component (e.g., Ca2+, SO42-, HCO3- and humic acid) could more or less alleviate the toxicity of S/nZVI. Furthermore, S/nZVI only exhibited slight toxic effect (<0.15-log after 1 h) in the presence of the mixed components. The same faint toxicity was observed for the aged S/nZVI, indicating that S/nZVI could lose its toxicity over time.

Multivariate relationships between microbial communities and environmental variables during co-composting of sewage sludge and agricultural waste in the presence of PVP-AgNPs.

This study evaluated the contributions of environmental variables to the variations in bacterial 16S rDNA, nitrifying and denitrifying genes abundances during composting in the presence of polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs). Manual forward selection in redundancy analysis (RDA) indicated that the variation in 16S rDNA was significantly explained by NO3--N, while nitrifying genes were significantly related with pH, and denitrifying genes were driven by NO3--N and TN. Partial RDA further revealed that NO3--N solely explained 28.8% of the variation in 16S rDNA abundance, and pH accounted for 61.8% of the variation in nitrifying genes. NO3--N and TN accounted for 34.2% and 9.2% of denitrifying genes variation, respectively. The RDA triplots showed that different genes shared different relationships with environmental parameters. Based on these findings, a composting with high efficiency and quality may be conducted in the future work by adjusting the significant environmental variables.

Factors influencing degradation of trichloroethylene by sulfide-modified nanoscale zero-valent iron in aqueous solution.

Sulfide-modified nanoscale zero-valent iron (S/NZVI) has been considered as an efficient material to degrade trichloroethylene (TCE) in groundwater. However, some critical factors influencing the dechlorination of TCE by S/NZVI have not been investigated clearly. In this study, the effects of Fe/S molar ratio, initial pH, dissolved oxygen and particle aging on TCE dechlorination by S/NZVI (using dithionite as sulfidation reagent) were studied. Besides, the feasibility of reactivation of the aged-NZVI by sulfidation treatment was looked into. The results show that the Fe/S molar ratio and initial pH significantly influenced the TCE dechlorination, and a higher TCE dechlorination was observed at Fe/S molar ratio of ∼60 under alkaline condition. Spectroscopic analyses demonstrate that the enhanced TCE dechlorination was associated with the presence of FeS on the surface of S/NZVI. Dissolved oxygen had little effect on TCE dechlorination by S/NZVI, revealing that the FeS layer could be able to alleviate the surface passivation of NZVI caused by oxidation. Aging of S/NZVI up to 10-20 d only slightly decreased the dechlorination efficiency of TCE. Although an obvious drop in dechorination efficiency was observed for the S/NZVI aged for 30 d, it still exhibited a higher reactivity than the bare NZVI. This indicates that sulfidation of NZVI did prolong its lifetime. Additionally, sulfidation treatment was used to reactivate the aged NZVI, and the results show that the reactivated NZVI even had higher reactivity than the fresh NZVI, suggesting that sulfidation treatment would be a promising method to reactivate the aged NZVI.

Physicochemical transformation of Fe/Ni bimetallic nanoparticles during aging in simulated groundwater and the consequent effect on contaminant removal.

To assess the fate and long-term reactivity of bimetallic nanoparticles used in groundwater remediation, it is important to trace the physicochemical transformation of nanoparticles during aging in water. This study investigated the short-term (within 5 d) and long-term (up to 90 d) aging process of Fe/Ni bimetallic nanoparticles (Fe/Ni BNPs) in simulated groundwater and the consequent effect on the particle reactivity. Results indicate that the morphological, compositional and structural transformation of Fe/Ni BNPs happened during the aging. In the 5-d short-term aging, Fe0 corrosion occurred rapidly and was transformed to ferrous ions which were adsorbed onto the surface of Fe/Ni BNPs, accompanied by the elevation of solution pH and the negative redox potential. In the long-term aging, scanning electron microscopy (SEM) images show that the particles transformed from spherical to rod-like and further to sheet-like and needle-like. X-ray diffraction (XRD) analysis reveals that the main aging product was magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) after aging for 60-90 d. Energy dispersive spectrometer (EDS) analysis demonstrates that the mass ratio of Fe/Ni increased with aging, revealing that Ni were possibly gradually entrapped and covered by the iron oxides. Besides, the release of Ni into solution was also detected during the aging. The reactivity of the aged Fe/Ni BNPs was examined by studying its performance in tetracycline (TC) removal. The aged Fe/Ni BNPs within 2 d kept similar removal efficiency of TC as the fresh particles. However, the removal efficiency of TC by Fe/Ni BNPs aged for 5-15 d dropped by 20-50% due to aggregation and oxidation of particles, and the removal efficiency further decreased slowly with the prolongation of aging time up to 90 d. This reveals that Fe/Ni BNPs were vulnerable to passivation in water environments.